A brief explanation will be made first, referring to FIG. 41, of the general configuration of an image reading apparatus (including both the one-side and two-side reading types) in which media having information to be read (below, referred to as documents or paper) are stacked on a hopper and are sequentially taken out from the lowermost document (bottom take-out type) and the information of the document is optically read (two-side reading type).
In the figure, the documents 1 stacked on a document hopper 3 are sequentially taken out from the lowermost document by the coaction of a paper feed roller 5 and a document separation pad elastically pressed against the same. Thereafter, the documents 1 are sent to a paper eject roller 13 via feed rollers 9 and 11 while being guided by paper guides (document stands) 17 and 19 and are ejected from there to the outside and stacked on a stacker 15. During this feeding operation, the information of the document is read by a first optical reading unit 21A and a second optical reading unit 21B. In the illustrated conventional example, the first optical reading unit 21A is arranged beneath a document passage 23 and reads the information (image) on a lower surface of the document, while the second optical reading unit 21B is arranged above the document passage 23 and reads the information (image) on the upper surface of the document. Note that, the first optical reading unit 21A and second optical reading unit 21B are constituted by light source lamps 25a and 25b; first and second reflection mirrors 27a, 29a and 27b, 29b; imaging lenses 31a and 31b; and one-directional image sensors 33a and 33b.
FIG. 42 shows the general configuration of a single reading unit type image reading apparatus which reads both surfaces of the document by inverting the same.
In the figure, parts corresponding to those in FIG. 41 are given the same numerals, and an explanation thereof will be omitted. Note that, in FIG. 42, the document 1 is shown supplied from the left side of the figure reverse to FIG. 41. The document 1 is sent in the right direction in the figure by a feed belt 41, and initially the image of the lower surface is read by the single reading unit 21. Note that, the reading unit 21 is moveable along the document stand 17, which performs a sub-scanning (in a direction orthogonal to a beam scanning direction, that is, the scanning of the document feeding direction). This sub-scanning is exactly the same in the case of FIG. 41 as well.
The document whose lower surface has been read is drawn in a direction A of the figure (left direction) by the feed belt 41. Before the rear edge is separated from reversing rollers 43, the feed belt 41 is reversed to pass the document between the reversing rollers 43, draw it in a direction B, and drop it on the reversing stand 45. Thereafter, the reversing rollers 43 are reversed and the document 1 is supplied onto the document stand 17 by coaction with the feed belt 41. At this time, the front and back of the document 1 are inverted from those at the first reading, and accordingly the image of the other surface (initial upper surface) can be read. After the completion of the reading operation, the feed belt 41 is reversed again, and the document 1 is fed rightward in the figure and stacked on the stacker 15. Note that, at this time, the passage switching lever 47 is opened to a position 47'. Although not particularly illustrated, if necessary, the passage switching lever is appropriately provided also at the portion of the reversing rollers 43.
There has been a rapid reduction of size and lowering of price of the main body of data processing apparatuses. Along with this, the reduction of size and lowering of price of the peripherals have been demanded. The image reading apparatuses are no exceptions. There was a problem in that with the conventional construction of image reading apparatuses, it was not possible to sufficiently respond to such demands for reduction of size and lowering of price, that is, the greater density of the mechanical components constituting the image reading apparatus and greater ease of fabrication and assembly of the same.
A bottom take-out type automatic paper feeding apparatus is provided, as shown in FIG. 43, with a paper feed roller 5 which comes into contact with the lower surface of a front edge portion of the document 1 stacked on the hopper 3 on the paper feeding side of the hopper 3. The conventional bottom take-out type automatic paper feeding apparatus is constructed so that this paper feed roller 5 is constituted by one roller and so that the front edge of the separation pad 7B, which is provided with flexibility, comes into surface-contact with the circumferential surface of the paper feed roller 5, so that the separated lowermost paper 1 is changed in its orientation slightly downward and fed out from a space between the paper feed roller 5 and the separation pad 7B.
The document fed out in this way is further fed while being held between a drive roller 9a and a driven roller 9b of the feed rollers 9. When it passes the reading portion a, an image of the image information on the paper is formed on a light receiving cells of the CCD's 33a and 33b by lenses 31a (31b) and read. The document is then ejected to the stacker 15 (FIG. 41) on the left side in that figure while being held between a drive roller 13a and a driven roller 13b of the eject rollers 13. In the conventional image reading apparatus provided with this type of construction, the feed rollers 9 and 11 (FIG. 41) and eject rollers 13 are synchronously driven by afeed motor 51, and the feed roller 5 is driven to rotate in the same direction (the same direction in a sense that when the feed roller 9 rotates in a direction supplying the paper, the paper feed roller 5 rotates in the direction supplying the paper as well. The reverse is referred to as the "reverse direction". The same is true also below) as the feed rollers 9 via two transmission gears 53 and 55. The apparatus further is constructed so that, by raising the peripheral speed of the feed rollers 9 to be slightly higher than the peripheral speed of the paper feed roller 5, the feeding speed of the paper after the paper is grasped by the feed rollers 9 is defined by the feed rollers 9. At this time, there is no looseness of the paper or the like between the feed rollers 9 and the paper feed roller 5.
The reason why the bottom take-out type automatic paper feed apparatus is used as an image reading apparatus is that the apparatus is constituted so as to read the lower surface of the document. In the conventional bottom take-out type automatic paper feed apparatus as shown in FIG. 43, however, if the amount of the paper which is stacked is increased or the paper is thick paper, there was a problem that errors such as double feed, paper misfeeding, or the like were liable to occur, so the paper feeding performance was unstable in comparison with the top take-out type automatic paper feeding apparatus. Namely, if the amount of the stacked papers is increased, due to the weight of the paper, the frictional force between the paper and the paper feed roller 5 and between the sheets of paper is increased, so that double feeding becomes easy, while if the paper is a thick paper, the passing resistance when the paper passes between the paper feed roller 5 and separation pad 7B becomes large, so that paper misfeeding easily occurs. Also, in the conventional apparatus of this type of construction, to stabilize the feeding of the paper, it was necessary to set the paper on the document stand in an inclined state so that the front edge of the paper at the lower end projects out in the paper feeding direction to a greater extent at the setting of the paper, and there arose a problem that the work load of the operator became greater.
Further, in the conventional apparatus, the paper feed roller and feed rollers are rotated in the same direction, and the paper is separated by the difference in the peripheral speed between the paper feed roller 5 and feed rollers 9, therefore a skew at the time of the setting of the paper (skew feeding of the paper) appeared on the reading image as it was. When the paper feed roller was rotated fast so as to improve the through-put, double feed was apt to occur, and therefore there arose another problem in that the improvement of the through-put was restricted.
For example, in the bottom take-out type automatic paper feeding unit mentioned above, to cope with documents having a wide range of paper quality, it was necessary to push the documents against the paper feed roller 5 and make the biasing force of the conveyance spring 7A for separating the paper variable. In the conventional apparatus, a variable mechanism of this conveyance spring having a construction as shown in FIGS. 44 and 45 has been used. Namely, there has been adopted a construction in which a fixed spring 7a and a moveable spring 7b are provided as the conveyance spring, the moveable spring 7b is provided around a pivot shaft 61 in parallel to the paper feed roller 5 so that it can swing and is biased by a biasing projection 63 in a direction to move it away from the paper feed roller 5. On the other hand, a rectangular cam 67 which is pivotally provided on a seat plate 65 of the fixed spring 7a in an eccentric position is made to abut against an engagement piece 69 formed by bending the moveable spring 7b. The rectangular cam 67 is pivoted by the lever 71, whereby the engagement piece 69 is pushed by the rectangular cam 67 in a counterclockwise direction in FIG. 44, to elastically press the moveable spring 7b against the paper feed roller 5.
According to this conventional construction, the moveable spring 7b is made to abut against the paper feed roller 5 and is separated therefrom by the operation of the lever 71, whereby it is possible to change the paper separation ability of the automatic paper feeding apparatus, but the lever 71 is projected from the rectangular cam 67, and therefore there arisen a problem in that the apparatus can not be constituted in compact size, and the number of parts is large, and thus the apparatus construction has become complex.
Also, in an image reading apparatus, a paper width detection sensor for detecting the width dimension of the fed paper is provided, but the reflectance of the surface greatly changes for each document, and therefore it is difficult to directly detect the document by an optical sensor. Thus, a sensor provided with a lever which physically comes into contact with the paper and swings is provided inside the paper passage. This type of conventional sensor is constructed, as shown in FIG. 46, so that a sensor bracket 81 is fixed on a paper feed frame by a screw 83, and a sensor arm 91 provided with a shielding plate 87 and a detection lever 89 on its two ends is pivotally fixed on a collar 85 secured to this sensor bracket by the screw. When the paper strikes the detection lever 89 from a direction indicated by an arrow X in the figure, the sensor arm 91 swings in the counterclockwise direction in the figure and the shielding plate 87 retracts from the light path of an opto-electric sensor 93 (the shielding plate 87 is usually positioned inside the light path of the opto-electric sensor 93 and cuts the beam), to detect the paper. Such a construction, however, had the drawback that the assembly of the sensor was cumbersome.
Also, the light source lamps 25 (25a, 25b) of the reading units 21 (21A, 21B) (FIG. 41) must be replaced when amount of the light is lowered, but the conventional attachment structure for enabling that replacement was one in which, for example as shown in FIG. 47, a lamp unit 97 constituted by the light source lamp 25 and its lamp frame 95 was inserted or detached into or from the side of the apparatus in a longitudinal direction of the lamp to attach or detach the same. Here, in FIG. 47, 92 is a socket which is fixed on the lamp frame 95 and supports the two ends of the lamp 25, and 99 is a plate spring attached to the main body. This plate spring 99 has a function of elastically pressing the inserted lamp frame 95 to affix the same. Reference numeral 17 is a transparent document stand, and 27a is a first reflection mirror. In the case of such a construction, however, it is necessary to provide an opening for performing the attachment and detachment of the lamp unit 97 to the side of the reading unit and the side of the apparatus frame, and it is necessary to reinforce the frame to make up for the strength lost by this opening, and therefore there is a problem in that the frame construction becomes complex. Since the lamp unit 97 was moved in the longitudinal direction, there existed a problem in the space required for the replacement work and the workability.
An object of the present invention is to solve the problems as described above. The invention has as its gist to make improvements in a bottom take-out type automatic paper feeding apparatus so as to more correctly perform the separation and supply of the paper, to increase the amount of the paper able to be stacked on the document stand, to smoothly perform also the supply of thick paper documents, and to enable the correction of the skew.
Further, so as to solve the above-mentioned problems, the present invention has as its gist to obtain a technical means with which the paper feeding portion and reading portion can be constituted in a compact size, the fabrication and assembly of the constituent materials are easy, and accordingly a document reading apparatus greatly reduced in size in comparison with the conventional apparatus is provided at a lower cost.